T helper cell (Th) function was assessed using peripheral blood leukocyte (PBMC) from 47 patients newly diagnosed with Hodgkins disease (HD). As well as from 10 patients, & 10 patients prostate cancer mononuclear cells. The PBL were stimulated in vitro with recall antigens (REC), HLA alloantigens (ALLO) and phytohemagglutinin (PHA). Four distinct patterns of Th responsiveness were detected in the HD patients: patients who responded to all three stimuli; patients who did not respond to REC; patients who responded only to PHA; and patients whose PBMC were refractory to all three stimuli. The more severely immun-compromised patients exhibited more sever hematologic parameters of HD. Of the 10 prostate cancer patients, four responded to all stimuli, five were unresponsive to REC, and one was unresponsive to REC and Allo. These findings suggest that defects in cell mediated immunity exist in patients with certain types of cancer. We also observed that more than 40% of HTLV-1 seronegative individuals who have been exposed to HTLV-1 exhibit T helper cell responses in their PBMC against HTLV-1 antigens.